A network storage system typically provides multiple user devices with access to one or more storage devices for recording and retrieving digital information. In conventional network storage systems, a storage server maintains data in a main (persistent) storage subsystem, which may be organized into one or more groups of storage devices, such as hard disk drives (HDDs) or solid-state drives (SSDs). Such drives begin to wear over time and eventually fail, e.g., after some finite number of read/write cycles or total data transfer threshold specified by a drive vendor. As drive wear-out or failure can lead to data loss, there is a risk associated with wear in storage systems. Providers of storage system services generally try to balance their tolerance for such risk with the drive replacement costs expected at the end of each drive's service life.
Historically, storage service providers have relied on using higher quality drives with relatively higher endurance levels and longer service lives to reduce wear-outs and replacement costs over time. However, the endurance of storage media in general is expected to decrease dramatically for some types of media, for reasons such as cost cutting. Consequently, the number of drive wear-outs and replacements are expected to increase. As the industry transitions to a state where drive replacements becomes more frequent, a simplistic approach that relies solely on drive quality or endurance levels might actually lead to increased costs for storage system operators.